CDL General Knowledge TestCombination Vehicles (if applicable)Easy
A driver is inspecting the air brake system of a combination vehicle. After building full air pressure, the driver applies the service brake. What is the maximum allowable air pressure drop in one minute for a combination vehicle?
- A3 psi
- B1 psi
- C2 psi
- D4 psi
Show answer & explanationAnswer & explanation
Correct answer: D. 4 psi
For a combination vehicle, the maximum allowable air pressure drop when the service brake is applied is 4 psi in one minute. This ensures the air brake system is functioning correctly without excessive leaks.
Why the other options are wrong
- A. This is too low; 3 psi is not the standard limit for combination vehicles.
- B. This is too low; a 1 psi drop would indicate an exceptionally tight system, but 4 psi is the standard limit.
- C. This is too low; 2 psi is the limit for single vehicles, not combination vehicles with more connections.
Air Brake Leakage Rate
The maximum allowable pressure drop in an air brake system over a specific time, indicating system integrity.
- Combination vehicles have a higher allowable drop due to more connections.
- Insufficient pressure drop indicates a leak.
- Checked with the service brake applied.
Memory trick: Four pounds for all the lines, keeps the brakes in fine designs.